The invention relates to a separating unit for a combine harvester.
A separating unit of the initially stated type is known from EP 0 522 267 B1. The separating unit, which operates according to the principle of axial flow, comprises a rotatably supported separating rotor disposed in a housing, the at least one separating grate which is equipped with openings and forms a separating region of the separating unit, and a cover having a closed jacket surface. The eccentrically disposed cover comprises, on the side thereof facing the separating rotor, a large number of guide elements which are arranged next to one another in a spiral shape coaxially to the longitudinal axis of the separating rotor, and which extend in sections in the radial direction of the cover.
A crop flow supplied to the separating unit rises due to the rotational forces of the separating rotor and moves along the housing in the axial direction and the radial direction, being guided by the separating rotor and the guide elements. The residual grain contained in the threshed mat that forms on the inner side of the housing is separated out in the region of the separating grate. The task of the guide elements arranged in a spiral pattern on the inner side of the cover is to guide the crop that is accelerated in the circumferential direction by the separating rotor to a delivery point. The centrifugal forces produced by the separating rotor act equally on the grain separated from the crop flow and on the straw contained in the crop flow. As a result, a compressing effect of the straw on the separating area of the separating grate can occur and cause a straw mat to form which prevents the grain from emerging from or passing through the straw mat.
The separating output varies depending on various parameters which are specific to the crop and to the separating unit. To increase the separating output of a separating unit described above, it is necessary to enlarge the separating area, increase the separating rotor speed, design the separating grates accordingly, and increase the number of revolutions of the crop in the separating unit. Enlarging the separating areas is constrained by the limited amount of installation space available, and so these measures quickly reach limits. Increasing the separating rotor speed and, therefore, the centrifugal forces is associated with an increase in the power uptake of the separating unit and results in increasing damage to the straw.